Published 4:40 pm, Monday, December 23, 2013

Rudolph the fictional reindeer was famous for his oddly colored nose, but his true-life cousins have eyes that change color depending on the season.

In the summer, the eyes of Arctic reindeer appear gold, and around Christmas they turn to a deep blue, biologists have discovered. It's not holiday magic, but rather a unique adaptation that helps these animals deal with the strange light conditions at the top of the world.

The reindeer's world is one of extremes. Above the Arctic Circle, Christmas falls in the midst of a 10-week period of perpetual twilight in which the sun never rises and the landscape is cast in bluish hues. But from mid-May to late July, the sun never sets, creating a long, endless day.

Biologists at the University of Norway in Tromso, one of the largest cities situated north of the Arctic Circle, studied the eyes and discovered that the color change occurs not on the iris, but on a reflective surface behind the central retina that's known as the tapetum lucidum.

Comet Lovejoy is expected to reach a pivotal point in its orbit Christmas Day when it comes closest to the sun. It will still be visible to earthbound skygazers, astronomers say.

The comet is not a sun-grazer like its sibling comet, ISON, which flew into the sun and vaporized last month.

"When the comet comes close to the sun, the solar winds push material off of it," said Jin Koda, an assistant professor in the department of astronomy and physics at Stony Brook University. Those winds force dust, ice and vapors off the core into the characteristic tail. Koda has captured some of the world's best photos of Lovejoy's journey.

Experts recommend evening viewing because the moon may hinder a good sighting before dawn. With a pair of binoculars Lovejoy should be easily visible around 6:30 p.m. until the end of the year.

"If you're looking east, the Big Dipper is scraping the horizon and its bowl is pointing on an angle up near the North Star," said comet tracker Dan Malerbo, an astronomer with the Buhl Planetarium and Observatory in Pittsburgh.

"Hercules is located to the left of the Big Dipper and has the shape of a keystone," he said. "This comet isn't getting too close to the sun. ISON was about 700,000 miles from the sun. This one is 70 million miles away."